While some of our perceptions of sound waves result from the physiology of the body and the interplay between the different ways we perceive sound, as mentioned earlier, other perceptions result from the physical behavior of sound waves. It is critical to understand the manner in which sound waves behave under any given set of circumstances.
The directionality of a sound wave depends on its frequency content. Higher frequencies are more directional, while lower frequencies are more dispersal. Simply put, high frequencies move in a straight line, while low frequencies spread out. This is why AM radio signals, which are broadcast at a lower frequency, seem to travel farther than FM radio signals (see Figure 2.13).